Surface properties, such as surface potential, surface charge quantity, surface charge density, surface electric field strength and specific surface area of a substance not only are widely used in the scientific research in fields such as colloid and interface science, material science, life science, soil science, ecology and environment science, but also have extensive use in chemical engineering fields such as paper making, cement, ceramics, chemical mechanical polishing (CMP), coal slurry, coating, cosmetics, food industry, mixed dispersion system. Thus, it is important to measure such substance surface property parameters.
In the existing technologies, typically indicator ion adsorption and potential titration are adopted for measurement of substance surface charge quantity. With respect to the indicator ion adsorption, one must first know the percentage of the total adsorption of H+ or OH− that involve electrostatic adsorption. However, since H+ and OH− also participate in adsorption of chemical bond, it is impossible to tell the percentage that involves the electrostatic adsorption. Thus, this method cannot measure the surface charge quantity of a system that contains variable charge under any pH values, any electrolyte concentration and any temperatures. The potential titration not only is not suitable for measuring the charge quantity of a system that contains permanent charge, but also its reliability is questionable even for variable charge system. Thus, there is no common measurement method of substance surface charge quantity that suits for various conditions and different systems. Further, no analysis apparatus is available that can conduct such measurement.
In the existing technologies, one method for determining substance surface charge density is based on the following formula:
      σ    0    =            T      C        S  
wherein, σ0 is surface charge density, Tc is surface charge quantity, and S is specific surface area.
Since this method requires the parameter of surface charge quantity, the issue faced in measuring the surface charge quantity must exist in determining the surface charge density. In addition, in the above formula of determining surface charge density, a measured data of specific surface area is also required. However, different specific surface area measurement methods may result in wide difference in their measurements. Thus, the reliability of the measurement is hard to control for a surface charge density measurement method that relies on the parameter of specific surface area.
The second method for determining surface charge density is to indirectly obtain a surface charge density value by using relevant formula of Gouy-Chapman upon obtaining a surface potential value of the substance. However, since currently there is no accurate measurement method of surface potential available that can be widely used, there is still difficulties to apply this surface charge density measurement method.
In the existing technologies, the electric field strength is determined based on the following formula:
      E    0    =                    4        ⁢        π            ɛ        ⁢          σ      0      
wherein, E0 is surface electric field strength, ∈ is medium dielectric constant, in which ∈ of water is ∈=8.9×10−10 C2/Jdm. Due to the dependence to surface charge density, the same issue faced in determining surface charge density also exists in determining surface electric field strength.
In the existing technologies, there are various measurement methods, e.g., normally adopted inert gas adsorption, ion negative adsorption, glycol ethyl adsorption, or glycerine adsorption and the like, to determine substance specific surface area. However, same substance using the various measurement methods results in great difference in the measurement. Even though specific surface area analyzer has been developed based on inert gas adsorption, the analyzer does not suit for measuring specific surface area of expandable substance.
Substance surface potential in the present application refers to potential on the initial surface of diffuse layer or OHP (outer Helmholtz surface). The existing measurement methods for substance surface potential include charge density method, negative adsorption method, positive adsorption method, secondary resonance generation method, pH indicator molecular method, fluorescence generation method, atomic force microscopy, and Zeta potential method, etc. All of the above methods have their own limitations. Charge density method, negative adsorption method, positive adsorption method and secondary resonance generation method are all only suitable for measuring surface potential value of constant charge sample of single electrolyte system under neutral condition. pH indicator molecular method, fluorescence determination method and atomic force microscopy will damage the status of the substance surface per se, and thus the reliability of the measurements is hard to control. Zeta potential method does not measure the surface potential; rather, it measures the potential on the shear surface during electrophoresis. The shear surface is away from the surface defined in the present invention. Zeta potential can be measured under different pHs, electrolytes and temperatures. Thus, in view that currently there is no surface potential measurement method that can be widely used under various conditions and is accurate, Zeta potential is the only choice as a surrogate of surface potential. However, extensive studies in recent years have found that, using Zeta potential method to determine the surface potential only has qualitative meaning. In additional, Zeta potential method has very rigorous requirements to the substance to be measured, i.e., it requires that the particle density of suspension colloid cannot be too high, and the particle size cannot be too large. Even the Zetaprobe-model Zeta potentiometer newly launched by Colloidal Dynamics, LLC (US) can only allow the highest particle density of 60% (volume density). Thus, it is impossible to achieve “original state” measurement for a system having higher density or solid particulate substance.
In view of above, currently there is no reliable and widely applicable method and apparatus that can measure substance surface charge quantity, specific surface area and substance surface potential. Thus, the measurement of substance surface electric field strength and surface charge density that relies on the measurements of substance surface charge quantity and specific surface area respectively also have same defects. Further, there is no method and apparatus in the existing technology that can be used to simultaneously measure the above five (5) parameters from a single experiment.